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Hydrostatics & Stability
The book explains how a ship floats and why it stays upright, and how naval architects check both. It begins with the shape of the hull and its description for numerical integration, and computes from it the displacement, the centre of buoyancy and the metacentre. It then follows the ship as weights are moved and loaded, as it trims, and as it heels to large angles under wind, waves and other heeling moments. The later chapters treat the checks that regulators require, from the inclining experiment to the intact and damage stability criteria, and then ships partly supported by a dock, the ground or a slipway, and the stability of multihulls, submersibles, high-speed craft and offshore units. Each chapter opens with a documented case and works its examples on reference hulls, and the reader can compute and check every number on the page.
Chapters
- Chapter 1
Hull form and its description
Describe a curved hull in numbers that can be calculated: what a floating ship must do, the principal dimensions, the axes and sign conventions of the book, the three reference hulls, the lines plan and the table of offsets, splines, NURBS surfaces and meshes, the displacement and its centres, the coefficients of form and the wetted surface, and the sectional-area and Bonjean curves. It opens with the losses of Vasa in 1628 and of HMS Captain in 1870, and with the righting levers worked out for Captain a fortnight before it capsized.
Compute areas, volumes, centres and second moments from a table of offsets, and judge which result to trust when two rules disagree: the trapezoidal and Simpson's rules, half stations and uneven spacing, running integrals, polygons and Green's theorem, and estimates of the error. It opens with Chapman's quarter circle.
- Chapter 3
Weight, buoyancy and flotation
Find how deep a ship floats and how much it can carry: buoyancy from the pressure of the water, the conditions of equilibrium, displacement, lightship and deadweight, the centre of gravity from a weight table, the draught and the tonnes per centimetre immersion, the effect of the density of the water, displacement from the draughts, reserve buoyancy and the load line mark. It opens with Samuel Plimsoll's campaign against overloaded ships.
- Chapter 4
Initial stability and the metacentre
Find whether a loaded ship is stable upright, and how stiff it is: the wedges of a small heel, the metacentre and the metacentric radius from the second moment of the waterplane, the metacentric height, the righting lever at small angles and how far it can be trusted, heel, list and loll and how they differ, the angle of list from the weight table and how a listed ship is brought upright, the angle of loll, and the longitudinal metacentre. It opens with the Eastland, which rolled over at its dock in Chicago in 1915, and returns to Captain and Monarch with the curves of stability that Attwood drew for them.
- Chapter 5
Moving, suspended and liquid loads
What the loads that are not fixed in the ship do to its stability: a mass moved, loaded or discharged and the height at which a load leaves GM unchanged; a load hanging from a crane, which acts at its point of suspension; the free surface of a liquid in a slack tank, its virtual rise of G and the fluid GM that the rules are applied to; cargoes that shift; and the complete loading calculation. It opens with the Herald of Free Enterprise, which capsized off Zeebrugge in 1987 with water across its vehicle deck.
- Chapter 6
Trim and longitudinal stability
How a ship trims and what its draughts are at the two ends: the reading of the draught marks, the centre of flotation and the moment to change trim; the change of trim when weights are moved, loaded or discharged, and loading to required draughts; draught limits and why moving weight cannot reduce the draught at the centre of flotation; the trim of a complete loading condition, and the limits of the small-trim methods; the change of trim with the density of the water; and the longitudinal stability of the ship. It opens with the Steel Flower, which touched bottom in the Welland Canal in 1996 while drawing more than the Seaway allowed.
- Chapter 7
Hydrostatic curves
The hydrostatic properties of the hull at every draught, collected as curves and tables: how they are calculated from waterplanes, how the slopes of the curves are related and how they can be checked, the jumps in the curves of a hull whose deck goes under water, quick formulas for KB and the curves of stretched hulls, and the Bonjean curves for a ship trimmed too far for the even-keel curves. It opens with the ironclad Virginia, which floated too high to fight as intended and, two months later, could not be taken up the James River.
- Chapter 8
Stability at large angles
The righting lever at any angle of heel and the curve of righting levers: KN and the lever of the weight, the trim that comes with the heel, the features of the curve, the cross curves of stability and how a loading condition is read from them, the corrections for the height and the transverse position of G and for free surfaces, the influence of freeboard and breadth, and a ship that is unstable upright. It opens with the car carrier Cougar Ace, which lolled to about 80° during a ballast exchange in 2006 and floated on its side until it was towed in and righted.
The moments that heel a ship, from wind, turning, crowding passengers, lifts over the side, towing and water on deck, and the angles at which it comes to rest under them; the work that the righting moment does against them, the area under the curve of righting levers, a moment applied suddenly or to a rolling ship, the reserve of dynamic stability and the weather criterion of the IS Code. It opens with the sail training yacht Concordia, knocked down by a squall off Brazil in 2010 with its lee doors open.
- Chapter 10
The inclining experiment
How the centre of gravity of a finished ship is measured: known masses moved across its deck, the heel read by pendulums, U-tubes or inclinometers, the plot of tangents and its fitted line, the displacement and KM of the waterline as inclined, and the lightweight survey that turns the ship as inclined into its lightship, with the accuracy of the result. It opens with the tour boat Ethan Allen, which capsized on Lake George in 2005 after its lightship had grown heavier and higher for four decades.
The criteria that a ship's curve of righting levers must meet: where the general criteria of the International Code on Intact Stability came from, the six requirements and the alternative for ships of wide beam, the loading conditions in which they are checked, limiting curves of KG, minimum GM and maximum deadweight moment, the special rules for grain in bulk, the stability booklet and stability instrument through which the master applies them, and the second generation criteria with a first-level check for parametric roll. It opens with the lake steamer Kuru, which capsized on Lake Näsijärvi in 1929, and returns to it with Rahola's criteria of 1939.
- Chapter 12
Damage stability
What happens when a compartment is open to the sea: permeability, the methods of lost buoyancy and added weight and why they give equal righting moments, sinkage, trim and list, the curve of righting levers after damage and the intermediate stages of flooding, the floodable length and the factor of subdivision, and the deterministic and probabilistic damage stability requirements of SOLAS, with the attained index of a cargo ship. It opens with the Titanic, whose loss in 1912 led to the first convention on the safety of life at sea.
Ships carried partly by a support: the support force and its two balances, one righting moment in three forms and why a metacentric height of a supported ship must state its basis, and the critical draught on the keel line; docking in a graving dock, with the critical instant, the largest trim and the loads on the keel blocks; floating docks and ship lifts; grounding on a falling tide, on a ridge, a flat bank or mud, and refloating by the neutral point; and the stages of an end launch, with tipping, the stern lift and the force on the fore poppet. It opens with the yacht Baaden, which capsized during its launch in 2014.
Craft whose waterplane or means of support differs from a ship's: catamarans and trimarans, with their large GM, short range and stability upside down; craft of small waterplane; submarines and passenger submersibles, whose stability when submerged is the height of B above G; semi-submersible drilling units at their transit and operating draughts, with the wind heeling moment and the area criteria of the MODU Code; and planing craft, hydrofoils and air-cushion vehicles under the HSC Code. It opens with the semi-submersible Ocean Ranger, lost with all 84 people on board in 1982.